Study on the variable frequency drive of an induction motor to reduce harmonics

Abstract

This thesis presents a method of designing and specify low voltage harmonics filters for variable frequency drives. The proposed method is used to measure the harmonics generated by VFD drive using harmonics analyzer and calculating then analyzing it to design active filter. The Variable Frequency Drive (VFD) is an electronics device to change utility power source to variable frequency to control AC motor in variable speed operation. It can be varies as per the load requirement. So, speed must be change as per increasing or decreasing the load. If supply voltage decreased, motor torques is also decreased. Motor speed is directly proportional to supply frequency, Hence, to maintain the speed supply voltage and frequency must be vary accordingly but during the switching sequence of the variable frequency drive generates harmonics. This thesis is intended to provide a basic understanding of Variable Frequency Drive (VFD) and reducing the VFD drive generated harmonics of the system by designing the active high pass filter in kessem sugar factory pump motor drives. This is done by using matlab Simulink software to show the effectiveness of the active filter. The reduced total harmonics distortion values in current and voltage are THDI=0.064% and THDV=0.017% respectively This makes reducing harmonics and as a result the VFD drives itself, the motor, the cable, total systems becomes protected from unwanted signals/harmonics and their life time will be increase if it is implemented. Output of the Simulink model with filter and without filter are shown, their out puts are compared and discussed based on results.